Secret files exposing evidence of widespread match-fixing by players at the upper level of world tennis can today be revealed by BuzzFeed News and the BBC.

The sport’s governing bodies have been warned repeatedly about a core group of 16 players – all of whom have ranked in the top 50 – but none have faced any sanctions and more than half of them will begin playing at the Australian Open on Monday.

It has been seven years since world tennis authorities were first handed compelling evidence about a network of players suspected of fixing matches at major tournaments including Wimbledon following a landmark investigation, but all of them have been allowed to continue playing.

The investigation into men’s tennis by BuzzFeed News and the BBC is based on a cache of leaked documents from inside the sport – the Fixing Files – as well as an original analysis of the betting activity on 26,000 matches and interviews across three continents with gambling and match-fixing experts, tennis officials, and players.

The files contain detailed evidence of suspected match-fixing orchestrated by gambling syndicates in Russia and Italy, which was uncovered in the landmark 2008 probe, and which authorities subsequently shelved. “They could have got rid of a network of players that would have almost completely cleared the sport up,” said Mark Phillips, one of the investigators. “We gave them everything tied up with a nice pink bow on top and they took no action at all.”

BuzzFeed News began its investigation after devising an algorithm to analyse gambling on professional tennis matches over the past seven years. It identified 15 players who regularly lost matches in which heavily lopsided betting appeared to substantially shift the odds – a red flag for possible match-fixing.

Four players showed particularly unusual patterns, losing almost all of these red-flag matches. Given the bookmakers’ initial odds, the chances that the players would perform that badly were less than 1 in 1,000. (Read more about the analysis here.)

Tennis is the latest sport to be caught up in allegations of corruption following the scandals that have engulfed world football and athletics.

It can today be revealed:

Winners of singles and doubles titles at Grand Slam tournaments are among the core group of 16 players who have repeatedly been reported for losing games when highly suspicious bets have been placed against them.

One top-50 player competing in the Australian Open is suspected of repeatedly fixing his first set.

Players are being targeted in hotel rooms at major tournaments and offered $50,000 or more per fix by corrupt gamblers.

Gambling syndicates in Russia and Italy have made hundreds of thousands of pounds placing highly suspicious bets on scores of matches – including at Wimbledon and the French Open.

The names of more than 70 players appear on nine leaked lists of suspected fixers who have been flagged up to the tennis authorities over the past decade without being sanctioned.

Nigel Willerton, who leads the Tennis Integrity Unit (TIU) set up to enforce fair play following the 2008 investigation, acknowledged that authorities had drawn a line under the evidence uncovered in the 2008 probe. The leaked files show that investigators implicated 28 players in suspected fixing and urged that they face a full disciplinary investigation. But Willerton said that tennis authorities took no action against them.

Players are being targeted in hotel rooms at major tournaments and offered $50,000 or more per fix by corrupt gamblers.

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He said the evidence was shelved because lawyers had advised that a new integrity code introduced in the wake of the investigation could not be enforced retrospectively. “As a result,” he said, “no new investigations into any of the players who were mentioned in the 2008 report were opened.”

Match-fixing has been explicitly outlawed by every previous version of the rules enforced by the game’s governing bodies. Moreover, since the new code took effect, tennis authorities have been warned that at least nine of the players who escaped further investigation have continued to play in suspicious matches.

Willerton insisted that the sport takes “a zero-tolerance approach to all aspects of betting-related corruption” and that “all credible information received by the TIU is analysed, assessed, and investigated by highly experienced former law-enforcement investigators.” And he pointed out that the Tennis Integrity Unit has disciplined 13 male players (all low-ranking) for fixing and banned five for life even though, Willerton said, prosecuting corruption cases is “notoriously difficult”.

“I can assure you that tennis is not treating this lightly,” said Chris Kermode, the president of the Association of Tennis Professionals, which governs the men’s game, last night. “The idea that tennis is not acting appropriately is ludicrous.”

But, as the 2016 Grand Slam season begins on Monday with the Australian Open, former integrity chiefs from within world tennis are breaking ranks to accuse the sport of failing to stamp out match-fixing.

Among them is Ben Gunn, the former police chief who led the review that recommended the formation of the integrity unit after the 2008 probe. He said the authorities had missed a “perfect opportunity” to clean up the sport and instead created a feeble and understaffed integrity unit that ignored key betting evidence. “What they did is a plastic solution which was not effective then and it’s not effective now,” he said.

Richard Ings, the former executive vice president for rules and competition at the Association of Tennis Professionals, said that match-fixing was a “regular thing” in the sport. He said the integrity unit’s response to the problem has been “very disappointing” and it is “far too secretive”.

The 2008 probe was triggered by a notorious match between the world number four, Nikolay Davydenko, a Russian, and the Argentine player Martin Vassallo Arguello, which attracted millions of pounds’ worth of highly suspicious betting triggered by accounts in Moscow.

The tennis authorities announced at the end of the investigation that they had found no evidence of rule-breaking by Vassallo Arguello or Davydenko. But the files reveal that Vassallo Arguello had exchanged 82 text messages at a previous tournament with the suspected ringleader of an Italian gambling syndicate that made hundreds of thousands of pounds betting on his other matches. Inquiries into the Russian gamblers who placed suspicious bets on Davydenko stalled when one threatened violence. These Italian and Russian gambling syndicates and another in Sicily were found to have placed suspicious bets on 72 matches involving the 28 players that the investigators flagged to the authorities.

Weeks after tennis authorities were handed the evidence, Bill Babcock, the head of the International Tennis Federation’s Grand Slam committee, declared that tennis was “healthy” and there was no corruption inside the sport. But the Fixing Files show that allegations of widespread corruption have continued to pour into the integrity unit in the years since.

The whistleblowers from inside world tennis who handed over the Fixing Files have asked to remain anonymous. But Phillips and two other investigators who conducted the probe said the evidence they found was “as strong as any evidence we’ve had” and the authorities “did nothing”.

In all, more than 20 gambling industry officials, international police detectives, and sports integrity experts told BuzzFeed News that world tennis is failing to confront a serious problem with match-fixing. BuzzFeed News and the BBC have chosen not to name the players whose matches have repeatedly been flagged for attracting highly suspicious betting, because without access to phone, bank, or computer records it is not possible to prove a link between the players and the gamblers. The integrity unit has the power to demand all that evidence from any tennis professional, yet many of the individuals whose activity attracted the most serious concern are still playing at a high level. Meanwhile, tennis has grown to a multibillion-dollar global phenomenon.

Today the secret evidence of corruption at the heart of the “gentlemen’s game” can be laid bare for the first time.

Peter Andrews / Reuters

Czarek Sokolowski / ASSOCIATED PRESS

Nikolay Davydenko of Russia (left) in the 2 August 2007 match against Martin Vassallo Arguello of Argentina (right) at the Orange Prokom Open ATP tennis tournament in Sopot, Poland.

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In pristine whites, Nikolay Davydenko looked in typically commanding form as he stepped out onto the clay court in Sopot, Poland, to defend his title as reigning champion of the Orange Prokom tournament. It ought to have been an easy victory: Davydenko was the world’s fourth-best tennis player, while his Argentine opponent, Martin Vassallo Arguello, languished far below him at number 87 in the rankings.

The wiry Russian played all his usual penetrating groundstrokes to win the first set and swiftly broke his opponent’s serve in the second. To the fans enjoying Polish kabanos sausages in the stands, play seemed to be progressing exactly as anyone would have expected.

But before the first ball had even been struck at the match on 2 August 2007, warning lights had begun flashing on the monitoring systems at the Betfair gambling exchange in London. Hundreds of thousands of pounds had begun flooding into the market that morning, backing Vassallo Arguello to win. By any objective measure Davydenko was the near-certain victor, but the amount of money stacking up against him was so significant that the odds had tipped to make his opponent the favourite to win.

Even after play began and Davydenko went a set and a break up, still greater sums of money continued crashing in against him. In total, £3.6 million was wagered on the game – more than 10 times the usual volume of cash for a tournament at that level – and much of the money being bet against the Russian was coming in from nine linked accounts registered to users in Moscow. Everything in the rankings and the way play was progressing on court pointed towards a resounding victory for Davydenko, and yet the Russian account holders seemed sure he would lose. What did they know that the bookmakers didn’t?

Davydenko (right) receives treatment on his foot during his second-round match with Vassallo Arguello at the Prokom Open, 2 August 2007. Czarek Sokolowski / ASSOCIATED PRESS

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Alarmed, the head of Betfair’s anti-corruption team in London picked up the phone to Gayle Bradshaw, the executive vice president of the Association of Tennis Professionals, to tell him something deeply suspicious was happening in Sopot. From the ATP’s office in Ponte Vedra Beach, Florida, Bradshaw got straight on the phone to the tournament supervisor in Poland, who rushed down to the courtside to watch the rest of the match. No sooner had he arrived than the contest took a dramatic turn.

Davydenko suddenly began hobbling. He repeatedly requested medical time-outs, complaining of pain in his ankle and then his toe, and he lost the second set to Vassallo Arguello. Three games into the third set, he threw in the towel and announced he was forfeiting the game due to injury.

Immediately after he walked off court, Betfair suspended the market and later announced – for the first time in its history – that all bets placed on the game were void. The market, it said in a statement, “quite clearly wasn’t fair”. It promised to turn over all its betting records to the tennis authorities.

The move caused a global sensation, and Davydenko was engulfed by the first major match-fixing scandal to hit world tennis. From the outset, the Russian insisted he was innocent. “I don’t know how to throw a match,” he told reporters. “I know that if you are in pain and can’t play on, you withdraw.” But the game had been shaken to the core, and the ATP announced it would conduct a full investigation.

Betfair and other bookmakers had been warning the ATP of the threat of gambling corruption in tennis for several years before the situation came to a head in Sopot. “This was something that we had been watching build,” recalled Betfair’s co-founder Mark Davies.

Bosses at the betting exchange felt they had to protect honest bettors who could lose huge sums of money if corrupt gamblers were rigging the market. Crisis talks were convened in London.

Six or seven players, including Davydenko and Vassallo Arguello, had repeatedly attracted suspicious betting activity, Davies recalled, and the management committee decided to take a drastic step: They would suspend all bets on those players.

The ATP’s own Richard Ings, who served as the association’s executive vice president for rules and competition until 2005, had compiled a list of 20 players who had been implicated in suspicious matches flagged by bookmakers – including both Davydenko and Vassallo Arguello. “There were consistently matches across the depth and breadth of men’s pro tennis with extremely suspicious shifts in betting odds,” Ings told BuzzFeed News and the BBC. “What became very clear is that, whilst there were lots of matches with suspicious betting patterns, you tended to see the names of the same players cropping up again and again.”

Players were widely rumoured to be “tanking” – deliberately forfeiting matches by not giving their best efforts – when they were tired or carrying minor injuries and wanted to preserve their energy for more important tournaments. Sometimes, it was said, players would carve up the spoils of victory: One would deliberately lose but get to keep the prize money, while the other would win and bag the coveted ranking points. Now, however, the ballooning phenomenon of online gambling meant billions of pounds were being bet each year on tennis, and a tip about a player’s intention to tank a match could yield vast winnings. Prize money at lesser tournaments can be paltry, and a year on the tennis tour can set a player back more than £100,000, making it tempting to cash in on the occasional fix.

“If you were to invent a sport that was tailor-made for match-fixing, the sport that you would invent would be called tennis.”

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Ings recalled that he had talked to a “great many players” about the problem and it became clear that fixing was “a regular thing within the sport”. He said five or so players told him they had been approached and offered sums “in the vicinity of fifty-thousand U.S. dollars to throw a first-round match at a middle-level ATP tournament”.

He began to realise that tennis was particularly vulnerable to corruption because tens of thousands of matches are played each year, with billions of pounds at stake on the gambling markets, and it only took one player to fix the outcome. “If you were to invent a sport that was tailor-made for match-fixing, the sport that you would invent would be called tennis,” he said. “It doesn’t take much effort on a player to throw a match without the opponent or the officials or the fans or even the media being aware. Where it does become apparent is in the betting market.”

Ings had wanted to find out why the same names kept cropping up in bookmakers’ reports of suspicious matches, but at that time officials lacked the power to investigate further. “Identifying whether someone has fixed a match is incredibly difficult without betting records, without access to telephone records, without access to financial transactions,” he said. So Ings introduced a new anti-corruption code that compelled players to hand over their phone and bank records to the ATP if they were suspected of fixing matches. Those powers were to be crucial in investigating the match in Sopot.

A team of former detectives and betting investigators from the British Horseracing Authority – whose integrity unit was considered the gold standard in world sport – were recruited by the ATP to get to the bottom of the Sopot mystery. They set up a temporary office on Shaftesbury Avenue in London’s theatre district, where they were led by Paul Scotney, the horseracing authority’s integrity director; Paul Beeby, its head of intelligence; and Phillips, its top betting investigator.

Scotney and Beeby were a pair of veteran organised crime detectives who in retirement had turned their hand to policing gambling corruption. “When you go to a murder scene and there’s a body, you know someone’s dead,” Scotney told BuzzFeed News. “On some betting markets you know there’s a body, and the Davydenko match was one of those. The odds just did not match with their rankings at all, and the amount of money that had gone into Betfair was totally disproportionate.”

While his colleagues set about preparing to interview the players and their entourages, Phillips was tasked with analysing the gambling data. He quickly found that about a fifth of the £3.6 million traded on the Betfair exchange had flooded in from a network of nine Moscow accounts, which were accessed from the same group of computers. “This strongly suggests that either all accounts were being controlled by one person or that the account holders were ‘working’ together,” Phillips noted in his formal statement to the ATP.

The betting odds should have reflected the fact that Davydenko was a far stronger player and had won the whole tournament in Sopot the previous year, but the sums of money bet against him were so vast that before play had even begun the odds were stacked heavily in Vassallo Arguello’s favour. By the time Davydenko was up two games to one in the first set, Phillips reckoned that Vassallo Arguello’s odds to win should have been around 5/1, which meant anyone betting on him would win £5 for every £1 wagered. Such odds would have implied a 17% chance that Vassallo Arguello would defeat Davydenko. But just 15 minutes into the match, one of the Russian accounts took odds for Vassallo Arguello’s victory at just 1/7, suggesting nearly 90% probability the underdog would win and only £1 could be won for every £7 bet on him.

Phillips concluded: “In almost 20 years of working in the gambling industry, as an on-course bookmaker, an odds compiler/trader, and as a betting investigator, I have never seen a match or race where so much of the money wagered was done at such unrealistic odds and by linked accounts.”

The betting analyst was then tasked with examining which other matches the Moscow ring had been betting on. His main brief was to crack the Sopot case, but he also took a wider look at suspect gambling patterns he was seeing on tennis matches across the Betfair exchange.

Meanwhile, the former detectives were tracking down the owners of the nine suspicious accounts. With the help of Betfair, they were traced to an affluent area of Moscow, and in January 2008, the investigators began calling the individual bettors.

The first account holder to pick up was a 31-year-old Muscovite called Julia Tsoy who had bet more than £260,000 against Davydenko by the time he had won the first set and would have almost doubled her money had Betfair not voided the market. She was hesitant in answering questions but acknowledged that she knew two of the other account holders. She said she researched the players from publicly available information before the match and had seen articles about Davydenko’s injuries. Then she told the investigators they needed to speak to her fiancé, Rustem, if they wanted to know more.

Rustem Ersainov owned at least two of the other accounts that had stood to make a huge profit on Davydenko’s loss, and he had started betting one minute after his fiancée had finished. He refused to talk about the bets he had placed and instead raged about Betfair’s decision to void the market. The investigators went on to contact the other Moscow gamblers but found them impossible interviewees. “The account holders were all drunk when we phoned them,” Phillips said. “One of them said people are going to get hurt over this. Some of them got angry, and some of them were just laughing.”

The computer sharing evidence, the betting patterns, and the interviews led the investigators to conclude that Ersainov was likely to be the ringleader in Moscow. They also found that the accounts he controlled had bet heavily on a string of suspicious matches involving other high-ranking players.

But shortly after the phone calls, Ersainov got in touch with Betfair and threatened “physical harm” to its main account manager in Russia if it didn’t call off the ATP investigators. Immediately, Betfair moved the manager out of the city. Neither Ersainov nor Tsoy could be reached for comment by BuzzFeed News.

The Betfair integrity unit were furious that the manager in Moscow had been put at risk. “We had advised the investigators how to approach the account holders, but they went in with their size 12s,” one source recalled. The unit’s manager wrote a stern email to the investigators. He said that Tsoy, another account holder, “and, in particular, Mr Rustam are three of our clients who did not wish to be contacted by the ATP” and that “the first two were cordial to you, but the last has provided us with an unequivocal warning that physical harm will be done to our employee. It is a significant problem which needs the sting taking out of it promptly in order to best help protect our employee. Would it be possible to send them a letter, at the soonest opportunity, apologising for contacting them?”

The manager got a terse email back from Beeby, reluctantly agreeing to send the letter, but complaining: “I have some serious concerns about what has been happening here,” adding that “I don’t think we needed to apologise to anyone for the action we took.”

The blockage in Moscow was a major setback to the investigation – particularly because Phillips was unravelling a trail leading from the Russian betting ring to a whole range of other suspicious matches where the account holders appeared to have used inside information to bet heavily on a particular player to lose. The investigators were becoming increasingly certain that what had apparently happened in Sopot was going on around the world. And it wasn’t just the Russian account holders cashing in. Phillips was confident he was closing in on evidence that gambling syndicates in north Italy and Sicily were also profiting on inside information.

He noted a clear pattern in the way play progressed during these matches that mirrored what had gone on in Sopot. “They were the set-and-break mob,” Phillips said. “The favourite will win the first set and go a break up in the second so the money comes in and the odds on him are as high as they can be – and then they’ll lose all their games from then on. That’s how it works.”

Meanwhile, the former detectives had also interviewed everyone connected with the match in Sopot. They spoke to the match umpire, who said Davydenko had not shownany sign of intending to throw the match during play, and the crowd had clearly not suspected anything untoward. “If he did tank the match he did it in a professional way and with style,” according to the report on what the umpire said. But the ATP manager who had rushed down to courtside after receiving the warning from Betfair noted that “it was very strange to see Mr Davydenko playing all return games in a very relaxed way and never getting close to break point.”

The physiotherapist who had attended to the Russian during his repeated medical time-outs told the investigators that the player had remarked: “What’s the point of staying on? The hard-court season is coming up.” Davydenko had then asked what the physiotherapist considered a “strange” question about his foot: “Is this a medical reason to retire?” He answered that it was, and Davydenko played three more games before pulling out. It seemed to the investigators as if his mind was made up that he wasn’t going to carry on playing some time before he withdrew.

If he did tank the match, the referee noted, he did it in a professional way and with style.

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An examination of the player’s medical records found that he had been diagnosed with an inflamed tendon in his foot, a common complaint among tennis players, three days before the match against Vassallo Arguello. Davydenko’s managers told the media that he had subsequently been diagnosed with a stress fracture. But while several doctors confirmed he had visited them shortly after the match, this diagnosis was not found in his records.

The detectives interviewed the Russian tennis star at the Sheraton Hotel at Frankfurt Airport in September 2007 along with his wife, his brother, and his coach. He denied having any relationship with the Russian account holders or being involved in any gambling. No one had approached him in advance about the Sopot match, and he hadn’t told anyone that he would retire injured. But he acknowledged he had told some other players, his wife, and his brother that he was carrying a foot injury. According to the notes of the interview, he said it was “normal, during a small tournament, that players might not try so hard during a match if they had an injury or, if there was a big tournament (such as a Grand Slam) coming up.” But this, he insisted, was not what had happened in Sopot. He also said he barely knew his opponent and they had not communicated before the match.

The player’s wife said she had not spoken to anyone about her husband’s foot injury. But his brother, Eduard, said he often received phone calls from journalists asking about Davydenko’s form and whether he was injured before a match, and that the player “does not keep his injuries quiet when speaking with Russian supporters”.

Davydenko declined to hand over his mobile phone – or those of his wife and brother – for forensic examination. On the advice of his lawyer, he resisted handing over his call records for so long that, by the time he was compelled to release them, much of the data was irretrievable. Investigators also suspected that he used more than one phone. “The situation with obtaining Davydenko’s complete telephone billings and/or an explanation for other phones he was suspected of using has not satisfactorily been resolved,” they noted.

The Russian’s lawyer, meanwhile, was fulminating about the way the investigators had treated his client. “What has happened here to Nikolay is just incredible,” Frank Immenga told ESPN. “From the first day, he was pushed into the corner and treated like a criminal.”

“I know that my client is truly innocent, so they will reveal nothing,” he said in another interview. “Davydenko was hurt; he had something on his foot; this was already seen before the match,” he continued. “There are people looking for information … When they find out that somebody is already hurt they are going to bet against him. That is exactly what happened.”

Vassallo Arguello, too, leapt to the defence of his opponent. “I don’t think the investigation is going to show that Davydenko was involved in anything,” he said in an interview. “Everything that happened on the court seemed very normal to me.”

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Davydenko’s Argentine opponent also denied in his interview with investigators that he had ever discussed the outcome of a match with anyone connected with betting, though he acknowledged gambling on soccer and women’s tennis. Unlike his opponent, however, Vassallo Arguello handed over his phone, and that of his coach. This led to a series of discoveries.

The first was a mobile number stored under the name Davydenko – which was curious because the Russian had said he and his opponent did not know each other. The rest of the discoveries were about matches that had nothing to do with Davydenko and, the investigators felt sure, would “form the basis for future investigations concerning this player”.

The detectives found that Vassallo Arguello had the numbers of several Italian Betfair account holders in his phone memory. The investigators sent the phone for forensic examination, which revealed text messages that the Argentine had deleted. Experts were able to recover the first few words of each of them.

Meanwhile, Phillips had identified a ring of Sicilian account holders who had cashed in on suspicious matches Vassallo Arguello had played during a previous European tournament. As with the Russian accounts, these were connected by computer sharing, suggesting to Phillips that they were being controlled by one person. The analysis of Vassallo Arguello’s phone showed he had exchanged 82 text messages with one of the account holders, a 43-year-old man called Fabrizio Guttadauro living in Sicily. And the phone numbers of other account holders were stored on Vassallo Arguello’s phone.

The first contact with Guttadauro was the day before an early match when Vassallo Arguello received a text message from him. As with all the deleted messages, investigators were only able to retrieve the first few words. They read: “This is my number, please if…” Then on the day of the match, Vassallo Arguello received another text: “Are you awake? Can I call you? Room 1.” Two more messages followed: “Don’t call from the mobile but from the room,” and “I would like to talk to you because of the match.”

To the investigators, it appeared that the two had then discussed the outcome on their hotel phones and agreed that Vassallo Arguello would approach his opponent, because at 1:15pm he texted the Sicilian with disappointing news: “He doesn’t want to do it. He intends to win and force…” But then 11 minutes later he sent another message: “I’ll come,” and, a little after that, “All okay.” The four Sicilian accounts then bet heavily on Vassallo Arguello to win the match. His opponent won the first set before losing in the second and third. The Sicilian bettors won more than £300,000 off the back of Vassallo Arguello’s victory.

The phone records revealed Vassallo Arguello had texted both the suspected Sicilian fixer and his opponent about the outcome of another match during the same tournament. The night before the game, the Argentine received a text from the player he was due to face saying simply, “Where are you?” Twenty minutes later, he texted Guttadauro, saying, “He’s replying to me this evening.” Later, the other player texted Vassallo Arguello giving his room number and asking, “Can we talk?” It was impossible to know what the opponents had discussed, but the following morning Vassallo Arguello sent another frustratingly truncated message to the Sicilian. “I’ve spoken with [him]. He asked me for a…” it said.

Sicilian money poured into the Betfair exchange before and during the match, and Vassallo Arguello lost heavily. As well as Guttadauro, the investigators linked another of the account holders to a number stored in the player’s phone. After the match, the other player texted Vassallo Arguello: “Martin, we have to talk. These guys are…” Four hours later, Vassallo Arguello wrote to Guttadauro, “Unfortunately he can’t be trusted.”

Reached by BuzzFeed News, Guttadauro initially said he did not know Vassallo Arguello and claimed his phone must have been hacked during the tournament. Then he called back, wanting to know if it was the Argentine who handed over his number, and whether he was in trouble with the FBI. He refused to answer any questions about his communications with the player, but added that under the right circumstances he might be able to provide “a scoop”. “You can make me an offer,” he said, “and then maybe I can tell you many more things.”

When they saw the text messages, the investigators told BuzzFeed News they thought the combination of the phone records and the betting patterns they had observed was “a smoking gun”. They found a further five highly suspicious matches played by Vassallo Arguello, on which the north Italian and Sicilian betting rings had gambled heavily.

Overall, the Russian and Italian gambling syndicates had bet on more than 72 matches in a way that Phillips thought looked overtly corrupt. There were 28 players whom Phillips suspected of rigging the outcome of those matches, with a core of 10 against whom he felt the case was overwhelming. And these were not all obscure games at small-time tournaments. Three of them had taken place at Wimbledon, and one was at the French Open.

Phillips prepared a report on the three suspected gambling syndicates in the spring of 2008. “It was absolutely conclusive to me that the players in my final report were fixing,” he told BuzzFeed News. He said he put in only the most egregious matches, but there were 40 or 50 more that he considered highly suspicious.

As for the gamblers apparently cashing in on the games, Phillips had found 11 highly suspicious Betfair accounts in Russia and concluded: “There is no doubt in my mind that these accounts are in receipt of inside information, at the very least, regarding Russian players.”

In Sicily, he found 10 betting accounts and 12 matches that warranted further investigation. “The betting patterns on some of these matches are nothing short of remarkable,” Phillips wrote. “The accounts appeared to know exactly how the games would pan out and backed the winning players at odds so far short of where they should have been that it made the betting markets on the matches completely farcical and obvious to anyone with betting analysis experience that the result was almost certainly a foregone conclusion.”

But the most disturbing group was in north Italy, where Phillips determined that six accounts were responsible for apparently fixing 29 matches. Eight players, most of them Argentine or Spanish, featured heavily on the list of suspicious matches – including Vassallo Arguello. “This group of accounts,” Phillips wrote, “are a bigger threat to the integrity of the sport than either the Russian or the Sicilian groups.” He added, “The way these accounts traded on some of these suspect matches, it would strongly suggest that both players in the match are involved in the conspiracy.”

When they drafted their report for the ATP following the Davydenko–Arguello match, the investigators concluded that a corrupt betting syndicate in Russia “knew … the outcome of the match in question before its conclusion” and that “it was this knowledge that allowed them to bet with such confidence prior to and during the match and would have allowed them to make a profit of £354,799 had Betfair not voided all bets.” There was “no doubt” in the investigators’ minds that advance word of Davydenko’s decision to retire injured had been passed to Moscow “from one of the players or their support”, but between the player’s refusal to turn over his phone and the threat to Betfair’s employee, the investigators had hit a brick wall. It just wasn’t possible to determine who the guilty party was in relation to this match.

So they concluded that the investigation had “been unable to find any evidence to support the possibility of Nikolay Davydenko or Martin Vassallo Arguello being involved in any corrupt practices surrounding their second-round match in Sopot on 2nd August 2007. It is felt that had we had the full support of Betfair account holders and all requested itemised telephone billings then this investigation may well have had a different conclusion.”

But the January after the Sopot match, the International Tennis Federation (ITF), the game’s overarching governing body, had launched a sweeping review of integrity across the whole sport, and that was still underway.

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The review was led by Ben Gunn, the former chief constable who had set up the British Horseracing Authority’s integrity unit, and Jeff Rees, a former detective chief superintendent with the Metropolitan police who had gone on to found the International Cricket Council’s anti-corruption department. The Sopot team handed over their evidence of the 72 suspicious matches they had found, and of the gambling networks in Russia and Italy. They knew Gunn well and trusted him to get to grips with it.

Armed with this evidence, the two detectives flew around the world interviewing players and observing tournaments. They concluded that, though tennis was not “institutionally corrupt”, “cheating at tennis for corrupt betting purposes” was the “most serious threat … to the core of the integrity of the sport”. In their landmark Environmental Review of Integrity in Professional Tennis, Gunn and Rees identified “specific concerns” about 45 of the matches that Phillips had highlighted, which they said warranted further investigation. Furthermore, they said, “Patterns of suspected betting activity have been noted on 27 accounts in two different countries.”

There was, the review warned, “no room for complacency”. World tennis must adopt a “co-ordinated and focused Anti-Corruption Programme with an adequately resourced Integrity Unit”.

Prize money at lesser tournaments can be paltry, and a year on the tennis tour can set a player back more than £100,000, making it tempting to cash in on the occasional fix.

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Bill Babcock, the ITF’s Grand Slam director who had overseen their investigation, publicly accepted the recommendation, but he put an optimistic spin on it. “This review is a positive statement,” he declared. “Tennis is a healthy sport. There are corruptors around the sport but not inside.”

What the world did not know was that, behind closed doors, a schism had opened up between Gunn and Rees over the proper model for the integrity unit. Gunn proposed including full-scale betting risk analysis capability to monitor the markets and proactively flag suspicious gambling just as Betfair had done on the Sopot match. It would be accompanied by a team of investigators to pursue cases against players once serious suspicions had been raised. Gunn’s model required six high-paid investigators, but Rees countered with a proposal for a much lighter-touch, less costly unit of just three. The Rees proposal would rely on tips from the gambling industry rather than initiating its own analyses or tracing heavily skewed bets back to their source.

The colleagues descended into a major shouting match, insiders say, with Gunn accusing Rees of “trying to do this with two men and a dog”. They were told to put both their proposals into their final report and allow world tennis to decide which it preferred.

Four months later, in September, Gunn learned that the authorities had opted for Rees’s approach, with half the number of investigators he had proposed, and no one to analyse betting data. Gunn was livid. “They were trying to do it, in my mind, with one hand tied behind their back,” he told BuzzFeed News and the BBC.

Willerton told BuzzFeed News that the decision not to employ a betting analyst was not a “soft option or a decision based on cost” but was “the recommendation of a highly qualified investigator”. And he cautioned against overemphasising the value of betting statistics, which he said should be treated as information rather than evidence: “Betting data alone is not sufficient to bring forward a prosecution; it has to be considered, assessed, and verified along with the TIU’s many other sources of intelligence.”

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The newly formedTennis Integrity Unit was unveiled in September 2008, headed by Rees. The same day, the ATP announced that it had found “no evidence of a violation of its rules by either Mr Arguello or Mr Davydenko or anyone else associated with the match” in Sopot. But no mention was made of the other alarming things the investigation had turned up: threats from the Moscow betting ring or the Argentine’s telephone links with Sicilian gamblers betting on other matches. As far as the public was allowed to know, the case was closed.

The investigators were then invited to hand over their wider evidence in a private meeting with the new unit at an exclusive hotel in London. They gave a PowerPoint presentation, published today by BuzzFeed News and the BBC, setting out their case.

The presentation laid out the text messages Vassallo Arguello had exchanged with suspected fixers and described the “very suspicious betting” by the Sicilian and Russian accounts. It listed all the matches and players that investigators believed were implicated in corrupt betting worldwide, and recommended that they all face a full disciplinary investigation.

“We said, ‘This is what you need,’ and we handed them over around five ring-bound files with all the hard evidence, and we also gave them the electronic evidence as well,” said Phillips.

“From my experience of working on dozens of cases for British horseracing, this evidence was very strong. It was really as strong as any evidence we’ve had.”

But Phillips, who now runs a private betting monitoring firm called Global Sports Integrity, recalled that Rees and his men “looked nonplussed” during the presentation and “didn’t ask questions”. Having gone in with high hopes, he said, “We finished the presentation and it was ‘Thank you, there’s the door.’”

Still, they continued to hope that the newly formed unit would pursue their evidence. “We waited and expected to hear that these players were being called into disciplinary hearings,” Phillips said. “Even if they had only done the half-dozen strongest, it would have sent the message that needed to be sent. But they did nothing.”

Shortly after the inception of the unit, a new code was introduced, and every professional player was forced to sign up to its terms. Like the previous anti-corruption rules, it outlawed all forms of fixing and gave investigators the power to compel players to hand over their phone and bank records if they came under suspicion. The burden of proof it adopted in order to merit a ban from the game was low. Investigators just had to establish that an offence had been committed based on the “preponderance of the evidence” – there was no requirement to prove the allegations beyond reasonable doubt, as a court of law would require.

But in their joint statement to BuzzFeed News, tennis authorities said the new integrity code applied only to future offences. A top US law firm “confirmed” that they could not apply new rules retrospectively, the statement said.

The ATP’s previous anti-corruption code had also plainly outlawed any “attempt to contrive the outcome or any other aspect of any event” – but the authorities said they had decided there was not enough evidence to bring any prosecutions under those rules. And they have not opened any new investigations based on the evidence handed over by the Sopot team.

The upshot was that the 28 players implicated in the 2008 report were never given a second look. Since 2009, the Tennis Integrity Unit has been warned again about nine of them.

The newly formed integrity unit also adopted a policy of withholding all details of its investigations from the public. “We accept that our confidentiality policy is not popular,” Willerton wrote in his statement to BuzzFeed News, “but we make no apology for it.” The policy, he said, protects players from “malicious allegations”, retains the element of surprise, and assures witnesses of confidentiality. But it also leaves the rest of world in the dark, even in cases where players have been punished, about what evidence went before it and on what basis its decisions were made.

The lack of transparency has rankled those who believe the sport is failing to confront a global problem effectively. “It’s a very secretive unit,” said Ings, the former ATP rules executive who set up its anti-corruption code. “We don’t know what it’s investigating, and when it does find violations the information that’s disclosed is so minimal that we really can’t get a handle on exactly how it’s operating,” he continued. “That’s a very disappointing aspect of the Tennis Integrity Unit at the moment.”

Meanwhile, the disbanded Sopot team carried on monitoring the markets and, from time to time, tried to warn the tennis authorities about matches that looked “hooky”.

After one such letter, Rees sent a stinging response.

“I have hesitated before writing to you, but I think I need to make you aware that in my view it is only a matter of time before a tennis player brings an action for libel against organisations, individuals, newspapers, those who make wild and irresponsible allegations,” he wrote, adding that he was already aware of the match that had been flagged. “As the Tennis Integrity Unit is charged with combating corruption in tennis we do, as I have already said, of course welcome any information about apparently suspicious betting patterns which helps us meet our responsibilities. However, as this and many other cases show, it is unwise to rely simply on betting patterns unequivocally to describe a tennis match as ‘fixed’.”

In the years since, other investigators, bookmakers, foreign police, and gambling regulators have continued to warn the unit about some of the same players – and many more besides.

BuzzFeed News and the BBC have seen a total of nine lists of suspected fixers handed to the world tennis authorities over the past decade, comprising more than 70 names. Of those, a core of 16 names appear repeatedly – in several cases as many as seven times.

At least six of the 15 players identified by the BuzzFeed News analysis of 26,000 matches have been flagged to tennis authorities by outside sources. The same analysis shows that the players whom the Sopot investigators first flagged to the Tennis Integrity Unit in 2008 have gone on to lose at least 112 matches where heavily lopsided betting appears to have significantly shifted the odds.

Willerton said the Tennis Integrity Unit did not need to employ a betting expert to perform this kind of analysis, because it got “immediate real-time access to gambling market intelligence” through cooperative agreements with the betting industry. But he downplayed the importance of this information, which he said was of limited use in prosecuting players. “Information supplied by betting operators can be an indicator of suspicious activity but is certainly not proof that corruption has taken place,” he said.

Bookmakers have told BuzzFeed News that, in many cases, when they tried to warn the Tennis Integrity Unit about suspicious matches they got no response. The tennis authorities often did not follow up to request in-depth information – such as the betting history and computer details of the suspicious gamblers – to which only bookmakers have access. Without that information, they say, a thorough investigation would be virtually impossible.

The European Sports Security Association, which collects suspicious betting alerts from bookmakers, has sent the Tennis Integrity Unit warnings from its members about suspicious matches involving 15 of the players whose names have repeatedly been flagged to the authorities. In one case, the integrity unit was sent four alerts about a particular player and warned to take note of his “relentless abuse”.

In addition, the European Sports Security Association alerted the Tennis Integrity Unit to 49 suspicious matches in the first three quarters of last year alone and warned in three successive reports that tennis attracts more dubious betting activity than any other sport.

By 2011, Betfair had flagged up at least 20 players who were attracting heavily skewed betting on their matches to the integrity unit – five of whom had also been in the Sopot files. No disciplinary action was taken against anyone named on the list, and in many cases, sources at Betfair said they heard nothing back from the integrity unit and were not asked to supply further information about the suspicious betting accounts.

“I mean, there were so many guys. And of course, it’s, like, big money in the game,” he said. “For one stupid match, just losing.”

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FederBet, a nonprofit sport betting watchdog, said it had flagged more than 20 matches to the tennis authorities in the last quarter of 2015 to no avail. “The problem of match-fixing in tennis is getting bigger and bigger,” said general director Francesco Baranca. He said bookmakers “try hard to fight against this because they realise they are losing a lot of money”, but he complained that the tennis authorities are unreceptive. Four other bookmakers also complained that their reports had met with inaction.

Willerton said that the integrity unit assesses “all credible information” and that investigations can take years. He added that “it is not the role of betting companies to make judgments about corrupt activity” and gambling sources “are simply not qualified to make statements about whether investigations have or have not taken place”.

International police sources, too, share evidence with the Tennis Integrity Unit. In 2013, a former player was prosecuted for corrupt betting on matches. As part of a plea bargain, he handed police a list of 28 players he said were involved in fixing. Six of them had previously been flagged to the tennis authorities by either the Sopot investigators or Betfair. He had placed asterisks against the names of seven players who he said he knew for certain had tanked matches. Officers sent the list to the integrity unit at Wimbledon, but say they heard nothing back. None of the players the fixer said he knew to be involved in corruption have been sanctioned. (One low-ranking player from the wider list was recently disciplined for failing to cooperate with the integrity unit in relation to unspecified offences.)

Last year, Italian police swooped in on two of the players who were flagged to the Tennis Integrity Unit by the Sopot team in 2008. Potito Starace and Daniele Bracciali were accused of match-fixing by judicial authorities in Cremona based on intercepted phone and internet conversations. Bracciali had allegedly discussed fixing a match in Rhode Island with an accountant who was later arrested, while the owner of a betting parlour had allegedly been overheard saying Starace agreed to fix the result of a final in Morocco in 2011. The evidence was passed to the Italian Tennis Federation, which briefly banned both players for life last August before its appeal court decided to clear Starace entirely and reduce Bracciali’s ban to one year in October. The federation did not publicly explain the appeal court’s reasoning. The pair, who deny the allegations, are still facing criminal charges in Italy. The Tennis Integrity Unit has not publicly sanctioned them for fixing. Both men deny the charges.

And a source in the Victoria police, whose sporting integrity unit guards against corruption at the Australian Open, said officers had tried to report concerns about fixing to the unit but had been frustrated by its unwillingness to discuss the problem. “The TIU need to be more proactive,” the source said. “Tennis is one of the easiest sports to corrupt, because there’s only one person up against the other, and because there’s so much money involved,” he went on. “You’re better off getting it out there and you might suffer a lot of short-term pain, but it’s better to weed out the problem.”

World tennis issued its first life ban against a player – the Austrian Daniel Köllerer – in 2011 for taking money to fix matches. No details of the charges against him, which he still denies, were provided. Speaking for the first time about his ban, Köllerer claimed that authorities were targeting him instead of pursuing stronger evidence against other players.

The Austrian was a deeply unpopular figure – known as “the most hated player on the tour” for brawling, spitting at opponents, and ridiculing ball boys. When he was eventually banned for match-fixing, he said that he had been approached three times – including one time at the French Open – by gamblers and asked to fix matches for sums ranging from $50,000 to $100,000. But he denied ever accepting the offers and said he had reported the approaches to the authorities.

Köllerer said that match-fixing was a widespread problem and claimed he knew of other players who were implicated. “They were losing matches on purpose,” he said. “Sometimes they were talking, like, in the next locker,” he went on. “I mean, there were so many guys. And of course, it’s, like, big money in the game,” he said. “For one stupid match, just losing.”

In a statement, the Tennis Integrity Unit said that the approaches Köllerer reported “proved to be from unidentifiable individuals on social media which could not be validated” and that he did not provide helpful information during his investigation.

The year after Köllerer’s ban, Rees stepped down from the unit and was replaced by Nigel Willerton, another retired senior detective from the “flying squad” – Scotland Yard’s armed robberies division.

Davydenko went on to enjoy a glittering career at the top of the game before retiring in November 2014. He reached four Grand Slam semi-finals and beat both Rafael Nadal and Roger Federer to win the ATP World Tour in 2009. When he announced his withdrawal from the game, he said, “Unfortunately, for some years now, I have been struggling with injuries. It’s hard for me to talk about it.”

His lawyer, Frank Immenga, told BuzzFeed News that his client had been cleared of wrongdoing. “Nikolay has finally been able to overcome the emotional distress suffered by this unjustified proceeding and does not want to be part of any further speculations,” he said. “Therefore, he will not be giving further answers to questions that he has answered already.”

Vassallo Arguello climbed to 47th in the world rankings in 2009 before his career began to tail off. He has never officially announced his retirement, but his last professional game was in 2011. He now works as a coach in Argentina. When contacted by BuzzFeed News, the player initially offered an interview but then stopped responding to calls and emails and never answered the questions that had been put to him.

Seven years after handing over their evidence, Gunn and the Sopot investigators still meet regularly at bars in London’s West End to share their frustration, over bottles of Sauvignon Blanc, at the missed opportunity to clean up the sport. “It would do a great deal of damage to the image of the game, but in order to clean it up they’ve got to clear up what corruption’s there now,” Beeby said.

“Tennis hasn’t got a problem because they don’t want to have a problem.”